#include<iostream>
#include<math.h>
#include<stdio.h>
#include <iomanip>
using namespace std;
int abs(int x){
    if(x<0){
        return -x;
    }else return x;
}
int main(){
    double x1,x2,y1,y2,dis,heigh,wid;
    while(cin>>x1>>x2>>y1>>y2){
    wid=abs(x1-y1);
    heigh=abs(x2-y2);
    dis=sqrt(wid*wid+heigh*heigh);
    cout<<fixed<<setprecision(2)<<dis<<endl;
    }
}
